This invention relates generally to the rotor windings of a dynamo-electric machine, and particularly, to endwinding ventilation schemes for machines with concentric rotor windings.
The rotors in large gas cooled dynamo-electric machines have a rotor body which is typically made from a machined high strength solid iron forging. Axially extending radial slots are machined into the outer periphery of the rotor body at specific circumferential locations to accommodate the rotor winding. The rotor winding in this type of machine typically consists of a number of complete coils, each having many field turns of copper conductors. The coils are seated in the radial slots in a concentric pattern with, for example, two such concentric patterns in a two-pole rotor. The coils are supported in the rotor body slots against centrifugal forces by metallic wedges which bear against machined dovetail surfaces in each slot. The regions of the rotor winding coils which extend beyond the ends (or pole faces) of the main rotor body are called "endwindings" and are supported against centrifugal forces by high strength steel retaining rings. The inboard end of each retaining ring is typically shrunk onto a machined surface at the end of the rotor body. The outboard end of each retaining ring is typically shrunk onto a circular shaped steel member called a centering ring. A section of the rotor shaft forging which is located underneath the rotor endwindings is referred to as the spindle.
Thus, the rotor winding can be separated into two major regions, the rotor body region within the radial slots in the rotor, and the rotor endwinding region that extends beyond the pole face, radially spaced from the rotor spindle. This invention relates primarily to ventilation schemes or circuits for the rotor endwinding region.
In order to reduce costs and machine size, rotating machine manufacturers are continuously seeking methods of obtaining more power output from a given volume of machine. Rotor winding thermal limitations are a major obstacle toward achieving this goal. Accordingly, more effective rotor winding cooling schemes facilitate the manufacturer's ability to achieve the desired higher power output.
Several rotor endwinding cooling approaches have been used in the past. Most of these approaches utilize longitudinally grooved copper windings where cooling gas enters the field turns from an open cavity via inlet ports at the sides of the turns, and then flows longitudinally along the grooves to discharge locations which are typically either chimneys in the rotor body or discrete baffled discharge zones under and around the endwinding. The gas in these baffled zones is typically discharged either to the air gap (i.e., the gap between the rotor and stator) via machine slots in the pole face, or to the area outside of the centering ring via openings in the centering ring. Some schemes utilize discharges through radial holes in the retaining rings.